Vibration damper for electric lines

ABSTRACT

Vibration damper for suspended cables of electric lines, comprising a pair of inertia members fixed to the ends of a resilient member or carrying cable, said resilient member being constituted by a length of wire rope formed by at least 18 wires twisted helically over a rectilinear central wire.

United States Patent [1l13,584,133

[72] Inventor Rodolfo Claren [56] References Cited My UNITED STATES PATENTS P 3.o52,747 9/1962 Clark etal. 174/42 [22] Filed Jan. 9, 1970 3,327,048 6/1967 Haro 174/42 [45] Patented June 8, 1971 43 0 3 969 Cl 174 42 73 Assignee A.Salvi& 0.5. p. A. H

Milan "aly 3,443,019 5/1969 Walker etal. 174/42 32 Priority Aug. 5, 1969 OTHER REFERENCES [33] Italy Bellino, Robert A., lnsulation, How to Select a Multicon- [31] 20605A/69 ductor Cable," Dec. 1967,pages 64 70. Copy in 174-128.

Primary Examiner- Laramie E. Askin At!0rneyBenjamin J. Barish [54] ya ES Qx E ELECTRIC LINES ABSTRACT: Vibration damper for suspended cables of elecalms g g tric lines, comprising a pair of inertia members fixed to the [S2] U.S.Cl 174/42 ends of a resilient member or carrying cable, said resilient [51] Int. Cl l-l02g 7/14 member being constituted by a length of wire rope formed by [50] Field ofSearch 174/42, at least 18 wires twisted helically over a rectilinear central PATENTEU JUN 8l97| 35841133 SHEET 1 BF 4 PRIOR 4R7 A Home y PATENTEUJUN 819m 3534.133

SHEET 3 BF 4 @Jp/fd C tlorne y PATENTEDJUN 8m: 3584.133

SHEET [1F 4 A Home y VIBRATION DAMPER FOR ELECTRIC LINES BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vibration damper for suspended cables, comprising a pair of counterweights or inertia members fixed to the ends of a resilient element or carrying cable and a clamp which engages the resilient element for attachment of the damper to a suspended cable subjected to vibrations due to the wind.

2. Description of the Prior Art My U.S. Pat. No. 3,432,610 already describes a vibration damper of this kind, in which the said two counterweights are substantially different and have a different mass and moment of inertia, and that the said clamp is secured to the carrying cable in a position such that the axial dimension of the carrying cable, measured from the clamp to the point of attachment of one counterweight, is substantially different from that measured from the clamp to the point of attachment of the other counterweight.

SUMMARY OF THE INVENTION The present invention relates to some constructive modifications aimed at further enhancing the optimum properties of the dampers described in my U.S. Pat. No. 3,432,610 and, above all, at obtaining greater uniformity in the characteristics thereof.

Starting from the consideration that the properties of a damper depend-as shown in.my U.S. Pat. No. 3,432,6l first of all, on the mass, the moment of inertia and the position of attachment of the counterweights, but also on the damping characteristics of the said carrying cable, the present invention now proposes a type of carrying cable which has substantially improved damping characteristics, especially as regards the uniformity of behavior, which is a fundamental characteristic for carrying out mass production. To this end, the carrying cable according to the present invention is characterized in that it is constituted by a length of wire rope formed by at least I8 wires twisted helically over a rectilinear central wire there being at least one short bush which tightly encloses and grips the twisted wires of the wire rope at a localized area thereof, leaving the major part of the twisted wires unenclosed.

According to a preferred embodiment, the 18 helically twisted wires are disposed in two layers, the inner one of which comprises six wires in direct contact with the rectilinear central wire, while the outer layer comprises l2 wires twisted in a helix of opposite sense to the helix of the wires of the inner layer.

BRIEF DESCRIPTION OF THE DRAWINGS The invention is in any case made clearer by the following description, with reference to the accompanying exemplifying drawings, in which:

FIG. 1 consists of a side view, partly in section, of a carrying cable of known type;

FIG. 2 is a view, similar to FIG. I, of a carrying cable according to the invention;

FIG. 3 is a side view, partly in section, of a complete damper according to the invention;

FIGS. 4, 5 and 6 are graphs respectively illustrating the behavior of a seven-wire cable of known type and of two alternate embodiments of the l9-wire cable according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In order to better understand the differences between the prior art and the present invention, in FIG. I is shown a cross section with a longitudinal view of a galvanized steel cable with seven wires, which is generally employed for conventional Stockbridge-type dampers. As can be seen, the cable is composed of a straight central wire over which six wires forming the outer layer of the cable are twisted. The stranding pitch P varies in function of the pitch diameter D of the cable. Each of the six wires of the outer layer bears on the straight central wire according to a helical profile actually defined by the stranding pitch P and by the diameter D.

FIG. 2 shows a cross section and a longitudinal view ofa 19- wire galvanized steel cable according to the invention. As will be seen, this cable differs from the sevenwire cable in that it has another layer of 12 wires twisted over the layer of six wires. The stranding pitch P is slightly different to the stranding pitch P. The sense in which the l2-wire outer layer is twisted is opposite to the sense in which the six-wire layer is twisted. Each of the 12 wires of the outer layer bears on the six wires of the inner layer along a helical profile (defined by the pitch P and by the diameter D not continuously but only at the points where it crosses the wires of the inner layer.

In the stranding stage, the six wires of the outer layer of the seven-wire cable and the I8 wires of the two layers of the 19- wire cable are subjected to a permanent deformation, called preforming, as a result of which when the stranding has been effected the wires tend.to close up, the six wires of the first layer exerting a pressure on the straight central wire and the 12 wires of the second layer exerting a pressure on the six wires of the first layer.

When the carrying cable of a damper is subjected to alternate strains in a plane, these being due to the oscillations of the counterweights, alternate tensile and compressive stresses occur in the wires.

In each section of the carrying cable, these stresses depend on the type and amount of deformation of the cable, on the distance of the considered section from the point of fixing in the counterweights, and on the distance of each individual wire of the section from the neutral plane perpendicular to the plane of the strains.

In view of the nonuniformity of the carrying cable, there occur-at the points of contact between the wires and in particular between the wires of an outer layer and those of the inner layer or the single central wire, during the oscillationsforces tending to cause the wires to slide with respect to one another, to which react the frictional forces due to the pressure of the wires between each other.

When this sliding takes place between the wires, there is a dissipation of energy which represents precisely the damping characteristic of the carrying cable.

. From what has been said, it is obvious how, for equal deformation of the cable, the energy dissipated, and therefore the damping characteristics of the cable, depend on the extent of the areas of contact between the wires, on the values of the coefficients of friction and on the pressure existing between the wires.

All these parameters, the effect of which is not necessarily linear, are not so easy to control when the carrying cables are produced.

According to the present invention, it has been found, surprisingly, and it has been verified experimentally, that the l9- wire cables having two stranding layers exhibit damping characteristics which are substantially more constant and uniform. This may be attributed, at least in part, to the fact that in a seven-wire cable the variation in the coefficient of friction or in the pressure of one or two wires has an effect on the total damping value of the cable which is far greater than that to be observed in a cable comprising 19 wires.

Practical tests carried out on 50 samples of dampers with a seven-wire carrying cable and on 50 samples of dampers with a I9-wire carrying cable, respectively, have given the results which can be found in FIGS. 4 and 5. Each position marked with an x represents the value measured in correspondence with the four resonance frequencies of each damper; each positioned marked by a dot represents instead the minimum value measured in the intervals between said resonance frequencies. The plotted curve represents the mean response. It is therefore extremely evident that, in the case of using a seven-wire carrying cable (H6. 4), the scattering of the response values is considerably greater than in the case of using a 19-wire carrying cable (HO. 5).

According to a further important feature of the present invention, the uniformity of behavior of the carrying cable can be further improved by fitting to the cable one or more suitably compressed short bushes apt to tightly enclose and grip the wires of the cable in localized area thereof, leaving the major part ofthe twisted wires unenclosed. It has been found that the provision of such bushes produces a reduction in the scattering of the response values as shown below, because it tends to equalize the friction between the wire strands.

FIG. 3 shows precisely a damper of the type described in my U.S. Pat. No. 3,432,6l0, to the carrying cable of which are fitted a bush A, on the central portion of the cable, and two bushes B, at the two ends of the cable. The bushes A and B are of metal and are clamped on the carrying cable by simple compression and deformation with a technique known per se. H6. 6 shows, in a similar manner to FIGS. 4 and 5, the response curves ofa group of 50 dampers with l9-wire cables, equipped with bushes according to the invention. The positive effect of the bushes on the reduction of the scattering of the response values can easily be observed by a comparison with the graphs of FIGS. 4 and 5.

lclaim:

1. ln a vibration damper, comprising a pair of inertia members secured to the opposite ends of a resilient member, the latter having a single clamp for attaching same to a suspended elongated member subject to aeolian vibration, the improvement wherein said resilient member is constituted by a length ofthe wire rope formed of at at least 18 wires twisted helically over a rectilinear central wire, and wherein there is at least one short bush which tightly encloses and grips the twisted wires of the wire rope at a localized area thereof leaving the major part ofthe twisted wires unenclosed.

2. Damper as in claim 1, wherein said 18 helically twisted wires are disposed in two layers, the inner one of which comprises six wires in direct contact with the rectilinear central wire, while the outer layer comprises l2 wires twisted in a helix of opposite sense to the helix of the wires of the inner layer.

3. Damper as in claim 1, wherein three bushes are fixed to said wire rope, respectively in the center and near to the anchoring points ofthe inertia members. 

1. In a vibration damper, comprising a pair of inertia members secured to the opposite ends of a resilient member, the latter having a single clamp for attaching same to a suspended elongated member subject to aeolian vibration, the improvement wherein said resilient member is constituted by a length of the wire rope formed of at at least 18 wires twisted helically over a rectilinear central wire, and wherein there is at least one short bush which tightly encloses and grips the twisted wires of the wire rope at a localized area thereof leaving the major part of the twisted wires unenclosed.
 2. Damper as in claim 1, wherein said 18 helically twisted wires are disposed in two layers, the inner one of which comprises six wires in direct contact with the rectilinear central wire, while the outer layer comprises 12 wires twisted in a helix of opposite sense to the helix of the wires of the inner layer.
 3. Damper as in claim 1, wherein three bushes are fixed to said wire rope, respectively in the center and near to the anchoring points of the inertia members. 